The present invention relates to a field controlled semiconductor device of SiC comprising superimposed, in the order mentioned, at least a drain, a highly doped substrate layer, and a low doped n-type drift layer. The device further comprises a highly doped n-type source region layer and a source connected thereto, a doped channel region layer connecting the source region layer to the drift layer and through which a current is intended to flow when the device is in an on-state. A gate electrode is arranged, upon applying a voltage thereto, to influence the charge carrier distribution of the channel region layer, and thereby the conductivity thereof, as well as a method for producing such a semiconductor device.
All type of field controlled semiconductor devices are comprised of, for example, field controlled transistors and field controlled thyristors.
Such semiconductor devices of SiC may especially be used as switching devices i power applications owing to the possibility of turning them on and off very rapidly. Such devices, made of SiC, are particularly well suited for high power applications, since such applications make it possible to benefit from the superior properties of SiC in comparison with especially Si, namely the capability of SiC to function well under extreme conditions. SiC has a high thermal stability due to a large bandgap energy, so that devices fabricated from material are able to operate at high temperatures, namely up to 1000 K. Furthermore, SiC has a high thermal conductivity, so that SiC devices may be arranged with a high density. SiC also has a more than five times higher breakdown field than Si, so that it is well suited to be the material in high power devices operating under conditions where high voltages may occur in the blocking state of a device.
Such field-controlled semiconductor devices may be divided into two main groups, namely so called normally-off devices and normally-on devices. This means that the channel region layer will have no conducting channel allowing electron transport from the source region layer to the drift layer when the gate electrode is laid on a zero potential, and that such a conducting channel is there when the gate electrode is laid on zero potential, respectively. Normally-off devices are more interesting and have more applications, since no voltage has to be applied to the gate electrode for cutting off the electron transport of the device, but the present invention covers both types of devices.
A field controlled semiconductor device of the type defined in the introduction is disclosed in U.S. Pat. No. 5,323,040. This device has vertical channel regions which are laterally restricted by trenches receiving a gate electrode. The channel region layer has to be very thin, in the order of a couple of .mu.m, for creating a normally-off device. The trenches in this known device have to be created by etching, and it is very delicate to etch to obtain such thin layers, so that it is difficult and complicated to provide a device constructed in that way with a normally-off characteristic.